st: Rare bug/feature in -graph,ylog-

I think I have discovered a rarely-encountered bug/feature in the Stata
-graph- command. (I use the very latest Stata 7 under Windows 98 SE.) It
appears that, if there is only one observation in the selected sample, and
-ylog- (or -xlog-) is specified, and the single y-value (or x-value) is in
the open interval between one and zero, then -graph- complains of
non-positive values. For instance, in the -auto- data, I might define a
variable -gpm- by typing:
. drop gpm

As you can see, -gpm- (gallons per mile) has values all in the open
interval from 0 to 1. If I then use this variable in a -graph- command with
one observation and the option -xlog- or -ylog-, then the result is as follows:

. grap weight gpm in 1,xlog
nonpositive values encountered
r(411);

. grap gpm weight in 1,ylog
nonpositive values encountered
r(411);

I get similar results if I restrict the -graph- to any other observation.
However, -graph- doesn't seem to mind if I type

. grap gpm weight in 1,xlog

. grap weight gpm in 1,ylog

in which case graphs are drawn. Nor is there any problem if more than one
observation is included, as follows:

. grap weight gpm in 1/2,xlog

. grap gpm weight in 1/2,ylog

It therefore seems that the problem -graph- has is specifically with the
non-positive logs in single-observation sample sets.

The bug/feature I have found is, of course, rarely encountered in day to
day statistical work, because very few people draw graphs with one
observation. (I discovered it today in the course of writing a cert script
for my -smileplot- package, downloadable from SSC, which plots P-values on
a reverse log scale against the corresponding estimates.) However, in the
interests of completeness, it would be ideal if this bug/feature was fixed,
before it confuses too many more unwary cert script writers.